Draft mechanism having roller pairs connected to draft ratio controlled motors by timing belts
FIELD OF THE INVENTION 
     The present invention relates to a draft mechanism for use on a spinning machine and more particularly relates to a draft mechanism which is capable of electrically controlling the draft ratios. 
     RELATED ART STATEMENT 
     The conventional draft mechanism usually includes, as shown in FIG. 3, a back roller pair consisting of a back bottom roller 1a and a back top roller 1b, a middle roller pair 3 consisting of a middle bottom roller 3a and a middle top roller 3b, and a front roller pair 4 consisting of a front bottom roller 4a and a front top roller 4b. A spinning machine provides a number of draft mechanisms of this sort in series on a machine frame. Although omitted in the drawings, rotation is transmitted to the respective rollers from a line shaft which is driven by a main motor and coupled with the respective bottom rollers, namely, with the back, middle and front bottom rollers 1a, 3a and 4a through a transmission mechanism including belts, chains, gears and so forth, stepping up the rotational speed in the order of the back rollers pair 1, middle roller pair 3 and front roller pair 4 to draft a sliver, which is supplied to the back roller pair 1, to a predetermined thickness until it reaches the front roller pair 4. 
     Therefore, the transmission of rotation from the line shaft to the respective bottom rollers involves back-lashes caused by the belts, chains, gears and the like, resulting in non-uniform drafting. 
     In addition, for alteration of draft ratio, the conventional mechanism requires complicated operations including changes of gear ratios and replacements of belts, chains and the like. 
     Therefore, the alteration of draft ratios require extremely troublesome efforts and meticulous skill, in addition to a need for the provision of a diversity of expensive gears of high precision machining to cope with various draft ratios. 
     OBJECT AND SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a draft mechanism which eliminates the back-lashes caused by belts, chains or gears during the transmission of rotation from the line shaft to the respective draft rollers, thereby precluding irregularities in drafting, while facilitating alterations of draft ratio. 
     According to the an embodiment of the present invention, there is provided a draft mechanism having a series of roller pairs each consisting of a bottom roller and a top roller, characterized in that the roller pairs have the respective bottom rollers separately and directly connected to the output shafts of motors, and the draft mechanism further includes a motor controller having a memory device for storing rotational speeds of the individual motors beforehand and adapted to control the respective motors according to signals supplied from the memory device. 
     The middle bottom roller may be driven and controlled by an apron which is surrounding around the middle bottom roller and an output shaft of a motor for the middle rollers. 
     In accordance with an embodiment of the present invention, there may be provided a draft mechanism comprising roller drive motors arranged to separately rotate bottom rollers of the respective sets of draft rollers each through a timing belt, and a controller for controlling rotational speeds of the respective roller drive motors. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a draft mechanism according to a first embodiment of the present invention; 
     FIG. 2 is a perspective view of a second embodiment of the invention; 
     FIG. 3 is a perspective view of a conventional draft mechanism; 
     FIG. 4 is a schematic block diagram showing a controller for motors; 
     FIG. 5 is a circuit diagram for controlling a motor; 
     FIG. 6a is a timing chart of transistors; 
     FIG. 6b is a diagram showing excitation of motor coils; 
     FIG. 7 is a perspective view of a draft mechanism according to the third embodiment of the present invention; 
     FIG. 8 is a perspective view of a mechanism in partially assembled state; and 
     FIG. 9 is a perspective view showing a relationship between the motors and controller. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     The present invention is described with reference to the drawings which show preferred embodiments of the invention. 
     Referring to FIG. 1, there is illustrated a draft mechanism according to a first embodiment of the invention, which includes, similarly to the conventional draft mechanism, a back roller pair 1 consisting of a back bottom roller 1a and a back top roller 1b, a middle roller pair 3 consisting of a middle bottom roller 3a and a middle top roller 3b having aprons 2a and 2b surrounding therearound, and a front roller pair 4 consisting of a front bottom roller 4a and a front top roller 4b. A number of drafting mechanisms of this arrangement are likewise mounted in series on a machine frame to constitute a spinning machine 
     In this first embodiment, however, the back bottom roller 1a of the back roller pair 1, the middle bottom roller 3b of the middle roller pair 3 and the front bottom roller 4b of the front bottom roller pair 4 are directly coupled with output shafts 7, 9 and 11 of motors 6, 8 and 10, respectively. 
     These motors are controlled by a controller 12 which includes a memory device for storing the rotational speeds of the respective motors and which controls the speeds of the motors according to the memory contents. More specifically, while storing the predetermined rotational speeds of the back, middle and front roller pairs 1, 3 and 4 for various draft ratios in the memory device, the memory contents corresponding to a desired draft ratio are taken out for each drafting operation, supplying signals from the memory device to the motor controller to operate same in such a manner as to control the respective motors to predetermined suitable rotational speeds. 
     In FIG. 1, the motors 5, 7 and 9 for the back, middle and front roller pairs 1, 3 and 4 are located side-by-side on the same side of the machine. However, in a case where the back, middle and front roller pairs 1, 3 and 4 are spaced too closely to each other to locate the motors side-by-side in tandem fashion, the output shaft 9 of the motor 8 for the middle roller pair 3 may be extended to locate the motor 8 in a staggered position or alternatively the motor 8 may be located on the opposite side of the machine (on the left side in FIG. 1). 
     A control device 12 for the motors 6, 8 and 10 shown in FIG. 1 will be described in detail. 
     In FIG. 4, a setting of a draft ratio and a setting of a spinning speed are carried out in the setting unit 13 having a display device 18. That is, the setting unit 13 is applied as a calculation control unit 14, a draft ratio between the motors M1 and M2 and a draft ratio between the motor M2 and M3 are inputted and a spinning speed of the motor M3 is set to make the speed instructions  ○1 ,  ○2  and  ○3 , respectively. 
     Reference numeral 15 denotes a micro-computer, 16 a motor driver and 17 an encoder. 
     FIG. 5 is a control circuit diagram for one motor (for example, the motor Ml) shown in FIG. 4. 
     In the timing chart shown in FIG. 6a, signals U +  to W -  denote an ON-OFF state of each of the transistors and an H-level indicated an ON-state of the transistor and an L-level indicates an OFF-state of the transistor. Three signals up to U +  to W +  may repeat an ON and an OFF in a short period in case of H-level. Either increasing or decreasing the time (t) of this H-level enables an amount of energization to be controlled and an acceleration or deceleration of the motor can be performed. 
     In FIG. 6b, each of the signals in each of the coils U-phase, V-phase and W-phase denotes an energized condition for each of the phases in the coil of the motor. In case that the signal is present above a central line, an electric current is flowed in a direction of current flowing into the motor and in turn in case that the signal is present below the central line, the electrical current is flowed in a direction of current flowing out of the motor. Accordingly, in case of the part A shown in the figure, the electrical current flows in a path of +42 VDC - U-phase coil - W-phase coil - OV. (FIG. 5) 
     In the present controller, a motor speed is detected by an encoder and the above-mentioned (t) is increased or decreased in such a way as the motor speed is coincided with a speed under an external command, and then the motor speed is accelerated or decelerated. 
     A timing of energization for each of the U-phase, V-phase and W-phase coils is determined in response to rotor position sensing signals u, v and W. 
     Illustrated in FIG. 2 is a second embodiment of the invention, which is an example where the back, middle and front roller pairs 101, 103 and 104 are located closely to each other to make the tandem positioning of the motors difficult. In this case, the apron 102a which is expanded around the middle bottom roller 103a in the foregoing embodiment is expanded around both the middle bottom roller 103a and the output shaft 109 of the motor 108 to function as a drive belt for the middle bottom roller 103a in addition to its original function as an apron, and the motor 108 is located in a position lower than the motors 106 and 110. 
     In other respects, the mechanism of this embodiment has the same construction and operational effects as the above-described first embodiment. 
     Thus, according to an embodiment of the present invention, there is provided a draft mechanism having a series of roller pairs each comprising of a bottom roller and a top roller, in which the roller pairs have the respective bottom rollers separately and directly connected to the output shafts of motors, and the draft mechanism further includes a motor controller having a memory device for storing rotational speeds of the individual motors beforehand and adapted to control the respective motors according to signals supplied from the memory device. According to another embodiment of the present invention, there is provided a drafting apparatus having a series of roller pairs each consisting of a bottom roller and a top roller, in which the roller pairs have the respective bottom rollers separately and directly connected to the output shafts of motors except a middle bottom roller, which middle bottom roller being connected to an output shaft of another motor by an apron expanding therebetween, and the draft mechanism further includes a motor controller having a memory device for storing rotational speeds of the individual motors beforehand and adapted to control the respective motors according to signals supplied from the memory device. Accordingly, it becomes possible to transmit rotation securely to the back roller, bottom roller and front roller free of back-lashes as experienced when transmitting rotation from the line shaft to the back, middle and front bottom rollers through a transmission mechanism using belts, chains, gears or the like, thus precluding irregularities in drafting. Besides, the draft ratio can be altered correctly in a simplified manner through control of the memory device, without entailing the complicate operations as conventionally required for replacement of belts, chains, gears or the like. 
     Furthermore, according to the draft mechanism of an embodiment of the present invention, it becomes possible to drive and control the draft ratios of a number of groups of draft mechanisms which are mounted in series on a machine frame for producing different types of threads independently of each other by the respective groups on a single spinning machine. 
     According to a third embodiment of the present invention, there may be provided a draft mechanism comprising roller drive motors arranged to separately rotate bottom rollers of the respective sets of draft rollers each through a timing belt and a controller for controlling rotational speeds of the respective roller drive motors. 
     Hereafter, the invention is described with reference to the drawings showing the third embodiment of the invention, a 4-line type draft mechanism. 
     Needless to say, the invention is not restricted to the 4-line type draft mechanism shown. 
     The 4-line type draft mechanism according to the embodiment, which is shown in an assembled view in FIG. 7 and in an exploded or disassembled view in FIG. 8, is constituted by a pair of top and bottom back rollers 202, a pair of top and bottom third rollers 203 of similar construction, a pair of top and bottom second rollers 205 having aprons 204a and 204b expanded therearound, and a pair of top and bottom front rollers 206. The rotational speed is stepped up in the order of the back rollers 202, third rollers 203, second rollers 205 and front rollers 206 thereby to form a thread by drafting a sliver which is fed to the back rollers 202 from a can, not shown, through a trumpet guide, taking up the thread by a take-up device to form a package. 
     As shown particularly in FIG. 8, the top roller 202a of the back rollers 202, the top roller 203a of the third rollers 203, the top roller 205a of the second rollers 205 with the aprons 204a and 204b, and the top roller 206a of the front rollers 206 are all rotatably supported on a shaft within a cradle cover 207 as shown in FIG. 7. The cradle cover 207 is pivotally supported by a support rod 208 at its one end on the side of the back top roller 202a. The support rod 208 is fixed on a top frame 209 through angles. 
     At the end on the side of the front top roller 206a, the draft cradle cover 207 is provided with a cradle hook handle 210. When the cradle hook handle 210 is operated to engage the draft cradle cover 207 with a locking portion of the top frame 209, the back top roller 202a, third top roller 203a, second top roller 205a with the apron 204a and the front top roller 206a are pressed against the back bottom roller 202b, the third bottom roller 203b, the middle bottom roller 205b with the apron 204b and the front bottom roller 206b, respectively, which are mounted on the top frame 209 to form a draft mechanism. 
     On the other hand, when the cradle hook handle 210 is operated to release the draft cradle cover 207, the latter can be turned about the support rod 208 to release the top rollers from the pressed engagement with the respective bottom rollers. 
     The back bottom roller 202b, third bottom roller 203b, second bottom roller 205b and front bottom roller 206b are independently rotated by motors 211 to 214 through flexible connectors comprising timing belts 215 to 218 which are passed therebetween, forming a thread by drafting a sliver gripped between the bottom rollers and the top rollers which are pressed against the opposing bottom rollers. 
     In this embodiment, the draft mechanism of the above-described construction is provided with a single roller gauge adjusting shaft 223 which meshes with bearing portions 219 to 222 of the back top roller 202a, third top roller 203a, second top roller 205a and front top roller 206a in an intersecting relation with the roller shafts thereof, and a single roller gauge adjusting shaft 228 which meshes with bearing portions 224 to 227 of the back bottom roller 202b, third bottom roller 203b, second bottom roller 205b and front bottom roller 206b in an intersecting relation with the roller shafts thereof. 
     These roller gauge adjusting shafts 223 and 228 are exactly same in construction, and provided with a coarse-pitch left-hand screw portion 229 which intersects the roller shafts of the back rollers, fine-pitch left-hand screw portion 230 which intersects the roller shafts of the third rollers 203, a fine-pitch right-hand screw portion 231 which intersects the roller shafts of the second rollers 205, and a coarse-pitch right-hand screw portion 232 which intersects the roller shafts of the front rollers 206. 
     Accordingly, for adjusting the roller gauges of the respective draft rollers depending upon the kind of the sliver and the fiber length, the knobs 233 and 234 of the roller gauge adjusting shafts 223 and 228 are turned to move the roller shaft bearing portion 219 to 222 and 224 to 227 along the screw portions of the roller shaft gauge adjusting shafts 223 and 228. As a result, the roller positions are shifted to establish desired roller gauges. 
     In the roller gauge adjustment, the timing belts 215 to 218 are elastically stretched or shrunk, absorbing variations in tension, so that there is no need for changing the positions of the motors 211 to 214. 
     Further, as shown particularly in FIG. 9, the motors 211 to 214 are connected to the controller 219, which controls the rotational speeds of the respective motors, for example, by control of an inverter, to effect the drafting at an optimum draft ratio in reference to preset total draft ratio, main draft ratio and feed draft ratio which have been determined beforehand on the basis of the kind and length of the sliver fiber. 
     As described in detail hereinbefore, the draft mechanism of this embodiment is provided with roller drive motors arranged to separately rotate bottom rollers of the respective sets of draft rollers each through a timing belt, and a controller for controlling rotational speeds of the respective roller drive motors. The motors which rotate the respective draft rollers are controlled by signals from the controller, rotating the draft rollers in such a manner as to establish a desired draft ratio. Therefore, the mechanism can cope with productions of various kinds of threads without necessitating to disassemble the machine or to employ complicated means over a long period of time for the purpose of adjustments. Besides, there is no need for providing spare parts for the gear box and line shaft. Thus, the invention not only permits a cost reduction and free alterations of the draft ratio but also contributes to a reduction of the number of steps in manufacturing process and an improvement in productivity.